Function streamResponse

packages/fetch/src/stream.ts:10–73

(
  response: Response,
)

}

export async function* streamResponse(
  response: Response,
): AsyncGenerator<string> {
  if (response.status === 499) {
    return; // In case of client-side cancellation, just return
  }

  if (response.status !== 200) {
    throw new Error(await response.text());
  }

  if (!response.body) {
    throw new Error("No response body returned.");
  }

  // Get the major version of Node.js
  const nodeMajorVersion = parseInt(process.versions.node.split(".")[0], 10);
  let chunks = 0;

  try {
    if (nodeMajorVersion >= 20) {
      // Use the new API for Node 20 and above
      const stream = (ReadableStream as any).from(response.body);
      for await (const chunk of stream.pipeThrough(
        new TextDecoderStream("utf-8"),
      )) {
        yield chunk;
        chunks++;
      }
    } else {
      // Fallback for Node versions below 20
      // Streaming with this method doesn't work as version 20+ does
      const decoder = new TextDecoder("utf-8");
      const nodeStream = response.body as unknown as NodeJS.ReadableStream;
      for await (const chunk of toAsyncIterable(nodeStream)) {
        yield decoder.decode(chunk, { stream: true });
        chunks++;
      }
    }
  } catch (e) {
    if (e instanceof Error) {
      if (e.name.startsWith("AbortError")) {
        return; // In case of client-side cancellation, just return
      }
      if (e.message.toLowerCase().includes("premature close")) {
        // Premature close can happen for various reasons, including:
        // - Malformed chunks of data received from the server
        // - The server closed the connection before sending the complete response
        // - Long delays from the server during streaming
        // - 'Keep alive' header being used in combination with an http agent and a set, low number of maxSockets
        if (chunks === 0) {
          throw new Error(
            "Stream was closed before any data was received. Try again. (Premature Close)",
          );
        } else {
          throw new Error(
            "The response was cancelled mid-stream. Try again. (Premature Close).",
          );